(1) Field of Invention
The present invention relates to a laser-light shield, and to a method for shielding a human body from laser light.
(2) Description of the Related Art
As is commonly known, in a laser (light amplification by stimulated emission of radiation), an artificial ruby, or other crystal, carbon dioxide, argon, nitrogen, or another gas or GaAs, GaAlAs, is stimulated or other semiconductor to emit a strong monochromatic light. The monochromatic light is amplified by a lens or the like. When a lens having a focal length of approximately 1 cm is used for the amplification, the light is focused to a point approximately 1/100 cm in diameter where the energy density is as high as tens of millions of watts per cm.sub.2.
It is well known to use laser light for piercing or cutting metal or ceramic parts and for a surgical operations.
Japanese Unexamined Patent Publication (Kokai) No. 57-47592 discloses a beam shielding device such as shown in FIG. 1. On this beam shielding device, four sheets 11a, 11b define an aperture for passing the laser beam. The surface area of this aperture can be varied by displacing the sheets 11a, 11b. The sheets 11a, 11b are made of a material which can absorb the laser beam. As an example, graphite or the like is mentioned in the publication.
A laser-light shield built of the sheets 11a, 11b must have a high shielding effect against a laser having a high energy density. In laser piercing of ceramics or an artificial jewels such as diamonds, rubies, or sapphires, laser light emitted from YAG (yttrium-aluminum-garnet, Y.sub.3 Al.sub.5 O.sub.2) is used to momentarily fuse the ceramic or jewel. Five or six pieces can be pierced at a high speed, e.g., one second. Leakage of the YAG laser light from the shield during such high speed operations may injure the attendant human operator.
Japanese Unexamined Patent Publication (Kokai) No. 58-4103 discloses a shielding plate 23 (FIG. 2) for shielding a laser beam 21. The shielding plate 23 is swivelled around an axis 24. When the shielding plate 23 is swivelled around the axis 24 by a certain angle, the laser beam 24 is emitted through an opening 22. The swivelling motion of the shielding plate 23 is limited by a stopper 25. The apparatus 20 is used as a surgical knife. The invention of the above publication is generally related to the structure of the apparatus 20 as summarized above.
The surgical knife, such as shown in FIG. 2, uses a carbon dioxide laser and is applied for bloodless operations in brain surgery, formative surgery, otorhinolaryngology, obstetrics, and gynecology. The surgical knife may also be combined with an end scope for surgical operations on digestive organs, lungs, or the urological tract under direct observation. Surgical knives are recently also being considered for genetic engineering and cytosurgery. The same ability of a laser to pierce the human body and thus serve as a surgical knife also makes it dangerous to the patient and attendant operators. The shielding plate 23 (FIG. 2) must stop the laser beam when the laser source (not shown) is actuated but the laser beam is not to be applied to the body. In addition, operators should be protected when the surgical beam is accidentally oriented to them.
American National Standard for the Safe Use of Laser (ANSI.Z136.1-1980) stipulates a standard for protecting operators from a laser but does not teach materials appropriate for a laser-light shield.
Metals, especially copper, are known as exhibiting good absorption of laser light.
It is known to improve the absorption of copper by vacuum-depositing gold black or platinum black on a copper body or depositing black paint or carbon black on the copper body. It is known to electrolytically plate chromium on a water-cooled copper box. The chromium-plated, water-cooled copper box has an improved absorption property. However, copper is not heat resistant.
A laser light shield must be resistant to exposure of strong energy over a long time, when high-energy laser light is to be used. Especially, in a cutting or welding device, the power of laser light is increased so as to enable working of a large-sized article.
In addition, a laser-light shield must effectively absorb the laser light which can be oriented to a metal body to various directions and then reflected from the metal body in various directions.